1. Field of the Invention
This invention relates to a wireless communications system, and more particularly, to a quadrature signal phase controller for controlling the phase difference between the in-phase signal and the quadrature-phase signal.
2. Description of the Related Art
Direct conversion receivers have a “zero-IF” structure” in which an intermediate frequency (IF) is 0 Hz (i.e. an IF is not used). The direct conversion receiver employing the zero-IF method or direct conversion method has a simpler circuit structure than a superheterodyne receiver. The direct conversion receiver is easy to be implemented as a single integrated circuit (IC) so the direct conversion receiver may be manufactured to be compact at a low cost.
The zero-IF structure and an image-rejection structure characteristically require an in-phase signal and a quadrature-phase signal that have the same amplitude and 90° delayed phases for signal conversion. However, the in-phase signal and the quadrature-phase signal do not generally have a precise phase difference of 90° due to many factors, for example, the manufacturing process, the supply voltage, or the operating temperature so that the signal-to-noise ratio (SNR) may deteriorate and thus the receiving sensitivity of a receiver may be deteriorated. Thus, there is a need for a quadrature signal phase controller capable of accurately controlling the phase difference between the in-phase signal and the quadrature-phase signal.